The present addition relates to improvements in the sealing device disclosed by U.S. Pat. No. 4,076,260. A sealing device of this nature is mounted on a rotating machine, such as a centrifugal pump, compressor or steam turbine of the type comprising a housing and a shaft emerging from the housing at at least one point. The sealing device comprises both a fixed sleeve, coaxial with the end of the shaft to be sealed, integral with the housing and housed inside a cavity formed at the end of the housing and housed inside a cavity formed at the end of the housing through which the shaft emerges, and a hollow rotating body. The hollow rotating body is defined by a member having an annular cross section fitted around the end of the shaft spaced from the fixed sleeve, and a substantially flat annular member joined thereto at its external edge, and the internal edge of which is loosely fitted around a portion of the sleeve which extends beyond the housing. The sleeve has an inside diameter greater than the diameter of the shaft, defining therefore with the latter a fluid-tight annular chamber which is limited on the machine side by an annular lip seal carried by the sleeve and normally being in fluid-tight contact about the shaft. The annular chamber connects with the cavity of the rotating body through a diaphragm tightly fitted to the shaft and across a path including a high pressure drop, formed between the sleeve and the walls of the hollow-body. The chamber is supplied with hydraulic fluid at a predetermined pressure which forms a liquid-tight sleeve in the fluid-tight annular chamber, and gives rise to a leakage rate towards the cavity of the hollow body across the path having a high pressure drop. The leakage fluid is projected by centrifugal force against the exterior peripheral wall of the hollow rotating body where it forms a liquid ring, the thickness of which is kept constant and less than the width of the annular flat member of the rotating body by means of a Pitot tube attached to the fixed sleeve. The Pitot tube comprises an arched shaped tubular body terminating at one end in a collecting orifice submerged in the liquid ring which faces the direction of rotation of the latter and terminating at the other end in the annular chamber.
Any excess liquid of the liquid ring is reintroduced into the fluid-tight annular chamber, which always remains filled with liquid, thus assuring sealing of the machine. The different elements of the sealing device are designed and dimensioned such that during operation, the pressure in the annular chamber is sufficient to lift the annular lip seal from the shaft. Therefore, during operation while the machine is rotating, sealing is assured by the liquid contained in the chamber, and in a neutral or nonrotating state, sealing is assured by the annular lip seal.
Such an annular lip seal functions satisfactorily in the case of a machine or pump containing a hydraulic fluid which is relatively neutral, cold or at a moderate temperature and pressure. But with a gas or an active liquid, for example, a corrosive, harmful liquid, or a liquid at a high temperature and pressure, the fluid-tight seal provided in the neutral or nonrotating state by such an annular seal is clearly inadequate. Such is the case, for example, with nuclear energy applications or with the treatment of dangerous chemical products, for which the fluid-tight seal must be absolutely perfect both in operation and in a state of rest.